An exhaust device for an engine provided with an oxygen sensor that enables detection of an oxygen component in an exhaust gas is known (for example, reference is made to Patent Literature 1 (FIG. 2)).
As shown in FIG. 2 of Patent Literature 1, an engine exhaust device (6) (The numerals in the brackets are the numerals used in Patent Literature 1. Same below.) is provided with an exhaust pipe (7) extending from an exhaust port of the engine and a muffler (8) coupled to a downstream end portion (7b) of the exhaust pipe (7). The downstream end portion (7b) is accommodated in the muffler (8). A three way catalyst (10) (referred to below as “catalyst”) is disposed in the exhaust pipe (7) to partition an inside of the muffler (8) on a downstream side of the catalyst (10) and thereby form a sensor chamber (8b). An O2 sensor (14) (referred to as “oxygen sensor (14)” below) is disposed in the sensor chamber (8b).
It is noted that the muffler (8) includes an expansion chamber that is imparted with a predetermined volume. When the oxygen sensor (14) is disposed in the expansion chamber of this type of muffler (8), it cannot be stated that sufficient detection accuracy for oxygen in the exhaust gas is enabled, for example, due to the fact that the exhaust gas leaving the catalyst becomes mixed with residual exhaust gas in the expansion chamber.
There is a need for a technique to enable more accurate measurement of oxygen contained in an exhaust gas in an exhaust device provided with an oxygen sensor.